[U-Boot] SPL Linux Boot V13

[Stefano Babic]

Rebased patchset to add Linux booting from SPL. As discussed
in the ML, this patchset does not make SPL common to all SOCs
to avoid breaking some architecture - this job will be done later
with a different patchset.

For this reason, a couple of patches moving files in the common/ 
directory are dropped - the other patches are not changed 
from V12.
(exception due only to rebase on current u-boot-ti)